What is the purpose of counter flashing?

Counter flashing serves a critical function in roofing systems, particularly where the roof meets vertical surfaces like walls or chimneys. Its primary purpose is to prevent water penetration at these joints. When installed properly, counter flashing is positioned over the base flashing, creating a barrier that directs water away from the roof penetration areas. This is particularly important because if water seeps into these joints, it can lead to significant moisture issues within the structure, such as mold growth, wood rot, and structural damage.

While enhancing aesthetic appeal might be a secondary benefit of counter flashing, its essential role is to ensure the integrity of the roofing system by providing an effective seal against water intrusion. Supporting ridge shingles and protecting against wind uplift are not the functions of counter flashing; those roles are typically addressed by other components of the roofing system.